BY JUSTIN RAYDecember 20, 1999 -- Follow the countdown and launch of a Lockheed Martin Atlas 2AS rocket and NASA's Terra spacecraft. Reload this page for the very latest on the mission.

SATURDAY, DECEMBER 18, 19992359 GMT (6:59 p.m. EST)
It was a long time coming but the cornerstone of NASA's Earth Observing System finally is in place. The Terra spacecraft, the $1.5 billion flagship for EOS, was successfully launched into space today aboard a Lockheed Martin Atlas 2AS rocket.

Terra is the first in a series of Earth-studying satellites NASA plans to launch over the next decade. The next, Aqua, is scheduled for liftoff late next year aboard a Boeing Delta 2 rocket from Vandenberg Air Force Base.

"This program is focused on developing an understanding of the total Earth system including the extent, causes and consequences and the regional consequences of global climate change," said Michael King, the EOS series senior project scientist.

Formerly known as EOS AM-1, Terra carries a suite of five sophisticated instruments from the U.S., Japan and Canada that will examine how Earth's oceans, atmosphere and land interact with each other.

"Terra will simultaneously study clouds, water vapor, aerosol particles, trace gases, terrestrial and oceanic properties, the interaction between them and their effect on atmospheric radiation and climate," said Dr. Yoram Kaufman, the mission's project scientist.

"Terra's objective is to start the first comprehensive and well-deserved check up of the planet."

The spacecraft was released from Centaur upper stage less than 14 minutes after the 1857:39 GMT (1:57:39 p.m. EST) launch. Terra's control computer then oriented the craft so the instrument deck was facing the Earth. The power-generating gallium arsenide solar array was deployed and the high gain communicaitons antenna was slated to be released Saturday evening. Controllers will put Terra through a testing and checkout period for 8 to 9 days prior to Y2K. As a safe guard, the craft will be put into safe mode during the transition to the new year. In early January, work to commission Terra will resume. Its science instruments should begin returning data in about three months.

"We're extremely pleased with the launch," said Kevin Grady, Terra's project manager. "The spacecraft is in good shape with all systems performing nominally. The mission is right on plan."

Terra's launch was delayed several times in the last two years by spacecraft-related problems, the need to double-check the rocket's upper stage engines, and more recently by ground software troubles on Thursday and high altitude winds today.

But in the end, the 46th consecutive success for Atlas was achieved.

This launch also wrote a bit space history. It was the first time a Centaur upper stage was used by an Atlas rocket from the Vandenberg Air Force Base launch site, the first time liquid hydrogen rocket fuel - consumed by Centaur - had used at Vandenberg, the first launch from Space Launch Complex-3 East since it was rebuilt to support Atlas 2-series rockets, Terra became the heaviest payload ever carried by Atlas and the liftoff ended the longest time a commercial Atlas rocket had waited on the launch pad - some 27 months.

"The vehicle had been on the pad for so long. It was almost surrealistic to see it actually in flight after 27 months on the pad," said Mike Benik, acting director of NASA's Expendable Launch Vehicle program.

The next launch for Atlas is scheduled for January 20 from Cape Canaveral Air Station, Florida. AC-138 will carry the U.S. Air Force's Defense Satellite Communications System B8 spacecraft into orbit.

2035 GMT (3:35 p.m. EST)
NASA ground controllers report the solar array on Terra has successfully deployed and communications are stable through the craft's low-gain antenna. Deployment of the high-gain antenna is expected at about 2330 GMT (6:30 p.m. EST) today. We will update this page once the HGA is out.

1926 GMT (2:26 p.m. EST)
NASA commentator George Diller says Terra's solar array is deploying as expected. It will be another hour or so before the array deploy is completed and the high-gain antenna release is confirmed. We will update this page a final time to confirm success of Terra's early operations in space.

1920 GMT (2:20 p.m. EST)
The orbit achieved by Terra has an apogee of 375 nautical miles, perigee of 353 nmi and inclination of 98.25 degrees. That orbit is near perfect. The pre-flight predications had an apogee of 373, perigee of 353 and inclination of 98.3 degrees.

1917 GMT (2:17 p.m. EST)
NASA says the release of Terra from the Centaur upper stage went as planned. The spacecraft rates at separation were normal.

1912 GMT (2:12 p.m. EST)
Over the next few minutes the Terra spacecraft will deploy its power-generating solar array and establish contact with ground controllers. Later, the satellite's high-gain antenna will be deployed.

1909 GMT (2:09 p.m. EST)
T+plus 11 minutes, 40 seconds. The twin RL10 engines of the Centaur upper stage have shut down as planned. Spacecraft separation will occur in just over two minutes to complete today's launch.

1907 GMT (2:07 p.m. EST)
T+plus 10 minutes. The Centaur will complete its firing in one minute, placing Terra into the desired low-orbit. Velocity currently 9,800 miles per hour.

1902 GMT (2:02 p.m. EST)
T+plus 5 minutes, 20 seconds. In the last 40 seconds, the Atlas sustainer engine was shutdown and the Atlas stage has separated from the Centaur upper stage. Centaur ignition confirmed. Centaur now in its single firing to place Terra into low-Earth orbit.

1900 GMT (2:00 p.m. EST)
T+plus 3 minutes. The booster package has been jettisoned from the Atlas stage. No problems reported so far in the flight. Sustainer engine of the vehicle still burning as expected.

1853:39 GMT (1:53:39 p.m. EST)
T-minus 4 minutes. The rocket's Flight Termination System is on internal power and armed for launch. The Centaur upper stage also has switched off ground power and gone to internal batteries.

1852:39 GMT (1:52:39 p.m. EST)
T-minus 5 minutes and counting. The Lockheed Martin launch team has picked up the countdown for launch today. The Atlas rocket is ready to conclude its 27-month wait atop Space Launch Complex-3 East and carry NASA's Terra satellite into near-polar orbit.

1849 GMT (1:49 p.m. EST)
The decision has been made to resume the countdown at 1852:39 GMT. However, upper level winds will not be verified acceptable until after the count picks up. If the winds are not acceptable for launch, the count will have to stop by T-minus 100 seconds.

1846 GMT (1:46 p.m. EST)
A poll by Lockheed Martin launch conductor Mark Ware has been completed. All systems were reported go with the exception of the upper level wind situation.

1842:39 GMT (1:42:39 p.m. EST)
Now ten minutes away from the scheduled point the countdown is supposed to resume in order to launch today. Upper level winds are still being worked.

1835 GMT (1:35 p.m. EST)
Lockheed Martin and NASA are likely to set 1857:39 GMT (1:57:39 p.m. EST) as the new launch time. That will give a 10-second buffer to the end of today's launch window.

1833 GMT (1:33 p.m. EST)
Officials are planning to target liftoff for the very end of today's launch window at 1857:49 GMT (1:57:49 p.m. EST). There is the chance that if the team working the upper level wind problem needs a few more moments, the countdown could resume at T-minus 5 minutes and counting at 1852:49 GMT, then cut off if the winds are still no-go.

1831 GMT (1:31 p.m. EST)
The Terra spacecraft has transferred to internal. Still awaiting a new potential liftoff time today.

1823 GMT (1:23 p.m. EST)
A launch team poll has been completed. All systems, technically, are go for launch. However, upper level winds are still no go. The countdown will remain holding a T-minus 5 minutes and liftoff will not occur as planned at 1833:25 GMT (1:33:25 p.m. EST).

1820 GMT (1:20 p.m. EST)
It appears the next set of upper level wind data should be available in about 20 minutes or so. If the data reveals acceptable high altitude wind conditions, the countdown could be restarted and the Atlas rocket launched before the close of today's window at 1857:49 GMT (1:57:49 p.m. EST).

1817 GMT (1:17 p.m. EST)
Still awaiting word on when the next upper level wind data will be received from the current weather balloon. Once the data is received, engineers will use the information to determine if the Atlas rocket can handle the conditions during launch.

1813:25 GMT (1:13:25 p.m. EST)
T-minus 5 minutes and holding. Countdown clocks have entered the final planned built-in hold for today's launch attempt. This was planned to be a 15-minute hold, however, the count will likely remain stopped here while officials await further upper level wind data.

The Atlas booster and Centaur upper stage are now fully fueled for launch, work that has been on going over the past 90 minutes. But given the super-cold temperatures of the liquid oxygen and hydrogen aboard the vehicle, the cryogenics will be replenished as the countdown continues. The Atlas was loaded last Saturday with its RP-1 fuel, a highly refined kerosene.

1811 GMT (1:11 p.m. EST)
Officials have just reported that the upper level winds are now unacceptable for launch. Additional data from high altitude weather balloons is expected before the end of today's launch window.

1806 GMT (1:06 p.m. EST)
Range Safety reports that all criteria is currently being met for launch. The final computer modeling shows that if a mishap occurred early in flight, the resulting toxic cloud would not pose a threat to the Vandenberg population. Also, the current modeling of the debris and air-start solid rocket booster nozzle cover impact areas indicate acceptable conditions for launch. However, there will be one further update for debris and nozzle covers prior to liftoff.

1803 GMT (1:03 p.m. EST)
Now 30 minutes from liftoff of the Atlas 2AS rocket and Terra from Vandenberg Air Force Base in California. Countdown clocks are continuing toward the T-minus 5 minute mark for a 15-minute built-in hold.

1758 GMT (12:58 p.m. EST)
U.S. Air Force launch weather officer Joe Kurtz has just reported that current conditions at Space Launch Complex-3 East are acceptable and expected to remain that way for liftoff in 35 minutes. The forecast for launch time has maximum winds at 22 knots, just below the limit of 24 knots. Temperature will be between 59 and 64 degrees F.

1757 GMT (12:57 p.m. EST)
Pitch and yaw steering programs have been loaded aboard the Atlas rocket's guidance computer. The programs are based on the latest upper level wind conditions the rocket should expect during the climb through the atmosphere.

Also, Range Safety is verifying the rocket's flight termination system ready for launch.

1745 GMT (12:45 p.m. EST)
As the countdown continues on schedule and without any problems in California for the launch of a Lockheed Martin Atlas rocket today, NASA officials have scrubbed tonight's liftoff of space shuttle Discovery due to a poor weather forecast. See our STS-103 Mission Status Center for further details later today.

1733:25 GMT (12:33:25 p.m. EST)
Lockheed Martin is now one hour away from launch of Atlas-Centaur 141 and NASA's Terra spaceraft. Fueling of the rocket continues to go smoothly and there are no problems with the vehicle, satellite, Western Range or weather.

1723 GMT (12:23 p.m. EST)
Five percent of the liquid hydrogen tank on Centaur has been filled. Today's launch will mark the first time a liquid hydrogen-fueled rocket has flown from Vandenberg Air Force Base. Centaur's twin engines will consume the hydrogen and liquid oxygen to boost Terra into the intended orbit around Earth.

1718:25 GMT (12:18:25 p.m. EST)
T-minus 60 minutes. All activities are continuing on schedule for today's launch of a Lockheed Martin Atlas 2AS rocket and NASA's Earth Observing System Terra spacecraft from Vandenberg Air Force Base in California. Fueling of the rocket is under way, there are no technical problems to report and weather conditions are forecasted to be acceptable. The count has one additional built-in hold at T-minus 5 minute leading to liftoff at 1833:25 GMT (1:33:25 p.m. EST).

Terra is a $1.5 billion mission to study the Earth's environment with a suite of five science instruments. Read an overview of Terra.

1715 GMT (12:15 p.m. EST)
The "go" has been given to start loading the liquid oxygen tank.

1714 GMT (12:14 p.m. EST)
The customary light coating of frost and ice is being to form on the Atlas stage. Just minutes ago the stage was bright and shiny silver, now it is becoming snow white.

1704 GMT (12:04 p.m. EST)
The chilldown conditioning is now under way of plumbing in preparation for loading liquid oxygen into the Atlas booster stage and liquid hydrogen into the Centaur.

1703:25 GMT (12:03:25 p.m. EST)
Now 90 minutes away from the scheduled liftoff time for the Atlas rocket and Terra spacecraft.

Today's launch will occur from Space Launch Complex-3 East at Vandenberg Air Force Base in California. Since its last launch in May 1995, the pad has undergone complete reconstruction to support the larger, more complex Atlas 2-series of rockets and their Centaur upper stages. The renovation contract was signed in late 1992 to build the new pad so Atlas 2 rockets could launch secret spy satellites for the National Reconnaissance Office from the U.S. West Coast, placing the craft into orbits that cannot be reached with launches from Cape Canaveral in Florida.

The old tower was demolished and rebuilt from the ground up. Construction was completed in September 1996 and the first Atlas rocket, the one flying today, was stacked on the pad in September 1997.

SLC-3E consists of the 230-foot tall mobile service tower that enclosed the rocket when it is at the pad, providing access and weather protection; the 170-foot tall fixed umbilical tower that supports lines connected to the rocket through which propellants are pumped to the rocket, as well as electrical power and conditioned air; the launch support building is a two-story structure contains support equipment; and the launch operations building where the countdown is controlled, located about 7 miles from the pad.

To date, there are three scheduled launches from the new pad: Terra today and two NRO payloads next summer and one about a year later.

1655 GMT (11:55 a.m. EST)
Preparations for the starting of liquid hydrogen fueling of Centaur are now under way. Meanwhile, the Centaur liquid oxygen tank is 65 percent full.

1653 GMT (11:53 a.m. EST)
U.S. Air Force launch weather officer Joe Kurtz says the approaching cold front should arrive in the Vandenberg Air Force Base area in about 30 minutes. The front will bring gradually increasing ground winds at the launch site. Currently, the winds at Space Launch Complex-3 West are at 13 knots. However, once the front moves into the area, the winds are forecasted to increase to 15 to 22 knots. The launch constraint is 24 knots. Overall there is a 60 percent chance of acceptable weather conditions during today's 24-minute, 24-seconds launch window.

1645 GMT (11:45 a.m. EST)
Pitch and yaw steering programs have been loaded aboard the Atlas rocket's guidance computer. The programs are based on the latest upper level wind conditions the rocket should expect during the climb through the atmosphere.

1643 GMT (11:43 a.m. EST)
The Centaur liquid oxygen tank is now 5 percent full as fueling operations are under way at Vandenberg Air Force Base in California. Weather conditions are looking favorable and there are no problems being worked.

1638 GMT (11:38 a.m. EST)
The go has been given to start loading super-cold loquid oxygen into the Centaur upper stage. This is the first of three propellant loading operations during today's countdown. The Atlas stage will be loaded with LOX starting in about 35 minutes. Liquid hydrogen fuel will then be pumped aboard the Centaur starting at 1724 GMT (12:24 p.m. EST).

1635 GMT (11:35 a.m. EST)
The Centaur upper stage's engines and liquid oxygen transfer lines are being chilled at this time to prepare for fueling operations. Also, the Atlas rocket's RP-1 fuel tank is being pressurized.

1603 GMT (11:03 a.m. EST)
T-105 minutes and holding. Countdown clocks have entered the first of two planned holds today. This will be a 30-minute hold. Five minutes before resuming the count, a readiness poll will be conducted of the launch team to verify members are ready for loading of super-cold fuel and oxidizer into the rocket.

Weather conditions, specifically winds, are acceptable for launch. The main threat is for winds to gradually increase with the passage of a weather front around launch time today.

1540 GMT (10:40 a.m. EST)
The 230-foot tall mobile service tower that has protected the Atlas rocket during its record setting 27-month stay at Space Launch Complex-3 East is retracted to the launch position. Preparations are continuing on schedule at Vandenberg Air Force Base in California for today's scheduled 1833:25 GMT (1:33:25 p.m. EST) launch.

The Atlas rocket to be launched today was assembled at SLC-3E in September 1997 to support pathfinder exercises at the newly rebuilt pad. Those tests to check the pad, ground support equipment and launch team were completed in April of 1998. However, the Terra satellite was grounded due to software problems, forcing the Atlas rocket to be placed in extended storage.

Lockheed Martin officials decided the best place to keep the Atlas was on the launch pad enclosed in the mobile service tower. The MST at Vandenberg is unlike the more open towers at Cape Canaveral Air Station's Complex 36 Atlas pads. The Vandenberg tower is often referred to as a building, fully enclosed and environmentally controlled. In addition, workers closed off the base of the tower and erected a tent around the base of the Atlas to protect the engines. Dry, warm air was also pumped into the tent.

Throughout the past two years the rocket has been coated with WD-40 to prevent corrosion. WD-40 was originally created 40 years ago for the Atlas ICBMs. X-ray tests were also performed every 90 days to check the structural integrity of the rocket's fuel tanks.

In May of this year when the decision was made to resume the launch campaign for Terra, Lockheed Martin reperformed tests and checkout of the pad and rocket for for today's mission, said Mark Ware, manager of launch operations at SLC-3. Launch pad validations were completed as if the rocket was never there. "It was like starting fresh."

When the work resumed the launch was planned for late July. However, when the Boeing Delta 3 rocket failed on May 4, another delay for Terra was triggered. The upper stage engine that caused the Delta 3 mishap is a similar version to the engines on the Atlas rocket's upper stage - Centaur. To ensure the engines on Centaur were safe to use, a pair of ultrasonic inspections were performed at the launch pad to check the engines' combustion chambers to see if the problem that doomed Delta 3 would affect Terra's ride. The inspections and later analysis concluded that the Centaur was ready for flight. The launch was rescheduled for today.

1430 GMT (9:30 a.m. EST)
The second countdown is under way at Vandenberg Air Force Base in California for launch of AC-141 and NASA's Terra spacecraft. Launch remains on schedule for 1833:25 GMT (1:33:25 p.m. EST) today.

Countdown clocks began ticking backwards at 1018 GMT (5:18 a.m. EST) today with the activation of the launch system computers at the launch pad. Later work has included a checkout of the Atlas rocket's flight termination system, a communications test with the orbiting Tracking and Data Relay Satellite System and tests of the Atlas' flight controls. Work is currently continuing to closeout of the payload fairing for launch.

Upcoming the launch team will review a weather briefing for rolling the mobile service tower away from the rocket. MST retraction is expected in about an hour. Also, an alignment will begin of the rocket's guidance computer.

0140 GMT (8:40 p.m. EST)
Lockheed Martin has cleared an Atlas 2AS rocket for launch Saturday to carry NASA's Terra satellite into space. A lengthy meeting Friday concluded that a software glitch which scrubbed Thursday's attempt had been resolved and similiar software problems did not exist in the ground launch sequencer.

If the launch does not occur on Saturday for some reason, it is unclear when the next attempt would be made. "We will cross that bridge when we come to it," NASA spokesman George Diller said. Sunday is not expected to be an option for the Atlas because the Western Range will use that day to reconfigure communications and tracking systems to support Monday night's (local time) launch of an Orbital Sciences Taurus rocket.

The main concern for Saturday will be ground-level winds. The forecast calls for a 60 percent chance weather will delay the launch.